When data is to be stored and retrieved from magnetic recording media, the parameters of the write channel and the read channel are generally optimized for the best combination of high storage density and low data error rate. During the write process, the write current, the write signal amplitude equalization and the write signal phase equalization are all adjusted to provide the best possible performance with the combination of the read/write transducer and recording medium used. With magnetic recording discs, these parameters are also advantageously adjusted for different track radii.
The parameters of the read channel are generally fixed at compromise settings during the read process, and these settings are not responsive to changes in the recording media, or in the case of magnetic discs, to track radii. Since there is no reference data signal to which the read signal can be directly compared, there are no convenient ways of analyzing the read signal to provide meaningful information which can be used for adjusting read channel compensation. In contrast, as indicated above, during the write process the written signal can be retrieved from the recording medium as it is written to compare it to the data signal so that the write channel compensation can be optimized. Although adaptive read channel techniques have been developed to allow for the optimization of the read channel compensation, these methods involve extensive digital signal processing requiring large amounts of computing power, which make them impractical for most data storage systems.